The present invention relates to handling and robotics systems, in general, and to such in semiconductor processing control systems, in particular.
Reference is made to FIG. 1 which illustrates a prior art process environment 10 in a semiconductor fabrication plant. In general, process environment 10 comprises a processing unit 2, such as a chemical mechanical polisher, at least one load/unload cassette station 4 (two are shown), an integrated metrology tool 6 and a robot 8.
The robot 8 transfers wafers to and from both the processing unit 2 and the cassette stations 4. However, the integrated metrology tool 6 requires its own handling system in order to transfer the wafer to be measured from the robot 8 to a measuring location on tool 6 and vice versa.
FIGS. 2A, 2B, 2C, 2D, 2E and 2F illustrate the operation of tool 6 and robot 8 using a handling system 16 to work with an integrated metrology tool having a measuring unit 15. One exemplary process environment uses the NovaScan 210 integrated metrology tool, commercially available from Nova Measuring Instruments Ltd. of Rehovot, Israel, and its handling system. The handling system 16 is composed of a bent arm 17 connected to a gripper 18. The latter can be any gripper which can hold a wafer. For example, it can be a vacuum gripper.
The arm 17 slides vertically on a vertical rail 14 and reaches above the measuring unit 15 in order to place a new wafer in a measuring position and/or to return a measured wafer to the robot 8. Between the uppermost position of gripper 18 and measuring unit 15 there is a supporting station 19 comprised of two supporting beams 24 and 25, each of which has a supporting base 26. Supporting beams 24 and 25 are connected to a rail 30 by a relative motion unit 32. Unit 32 is designed to provide relative motion to supporting beams 24 and 25 such that they move toward and away from each other, as indicated by arrows 34 and 36. Supporting station 19 is connected to the measuring unit 15 by a solid connector 54.
As shown in FIG. 2B, with supporting beams 24 and 25 in their most separated positions, gripper 18 can freely pass through the buffer station 22, even when loaded with a wafer. As shown in FIG. 2C, with supporting beams 24 and 25 in their closest positions, a wafer can be held on each of supporting base 26 and gripper 18 cannot pass through.
In operation, and as shown in FIG. 2D, the robot 8 arrives at integrated tool 6 loaded with a new wafer W on an arm 9. At this point, handling system 16 is waiting in its uppermost position. Robot 8 places the wafer W on supporting bases 26, after which, as shown in FIG. 2E, handling system 16 moves down and picks up the wafer W. Robot 8 then leaves integrated tool 6 to conduct other missions while handling system 16, loaded with the wafer W, continues down, until, as shown in FIG. 2E, it places the wafer, working surface down, in a measuring position on the measuring unit 15. Typically, the measuring position includes supports which support the wafer on its edges (not shown). Since supporting beams 24 and 25 have moved towards and away from the plane of the paper, the supporting station 19 is shown in FIG. 2F with dashed lines.
It is noted that robot 8 leaves tool 6 empty and must arrive at tool 6 unloaded in order to take back a measured wafer. Thus, robot 8 is not optimally exploited, i.e., a disadvantage considering that the robot 8 is the xe2x80x9cbottle neckxe2x80x9d in process environment 10 (FIG. 1).
Prior art systems solve this problem in multiple ways. One exemplary robot is the DBM 2400 series of Equipe Technologies, Mountain-View, Calif., USA. This robot has two separate arms. A second exemplary robot is the PerMer 6100 robot of Cybeq Systems, Sunnyvale, Calif., USA. The robot can hold two wafers, one on each side of its arm, and rotates the arm 180 degrees in order to switch wafers. For both prior art systems, the robot arrives at the supporting station loaded with a new wafer, and the free arm or side faces the supporting station. The free arm (side) loads a processed wafer from the supporting station, after which, the arm (side) with the new wafer is loaded onto the supporting station. The robot then returns loaded with the processed wafer.
It will be appreciated that these solutions require additional footprint since, during their operation, the two arms (sides) are loaded with both new and processed wafers. This may be a drawback in crowded processing environments.
It is therefore an object of the present invention to overcome the aforementioned limitations of the prior art.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a buffer station for a wafer handling system. The handling system has a general path along which it moves when handling the wafer and the buffer station includes at least one pair of supporting elements and a motion unit. The supporting elements together are capable of supporting at least two wafers therebetween and they are located so as to support the wafers within the general path. The motion unit provides relative motion to the supporting elements such that, in a first mode, the supporting elements support any of the wafers placed thereon within the general path and, in a second mode, the supporting elements are sufficiently separated so as not to disturb the motion of the handling system when the handling system holds a wafer. Typically, the supporting elements include at least two supporting bases each capable of holding a wafer thereon when the supporting elements are in the first mode.
Alternatively, in accordance with a preferred embodiment of the present invention, the buffer station includes at least two pairs of supporting elements each capable of supporting at least one wafer therebetween and located so as to support the wafer within the general path and one motion unit per pair of supporting elements. The motion unit shifts its associated pair of supporting elements in and out of the general path and, when said supporting elements are in the general path, provides the relative motion to its associated pair of supporting elements described hereinabove.
Additionally, each supporting element includes at least one supporting base each capable of holding a wafer thereon when the supporting elements are in the first mode.
There is also provided, in accordance with a preferred embodiment of the present invention, a processing unit for processing at least one semiconductor wafer. The unit includes a processing station for processing the wafer, a measuring station for measuring the wafer, a robot for moving the wafer between the processing and measuring stations, a wafer handling system and a buffer station. The wafer handling system operates in conjunction with the measuring station and moves the wafer to and from a measuring location on the measuring unit. The buffer station is associated with the wafer handling system and receives measured and unmeasured wafers. This enables the robot to arrive at and leave the measuring station with at least one wafer thereon. The buffer station can be any of the buffer stations described hereinabove.
Additionally, in accordance with a preferred embodiment of the present invention, the buffer station also includes a unit which enables the robot and the wafer handling system to operate generally independently of each other.
Further, in accordance with a preferred embodiment of the present invention, the processing unit also includes a pre-alignment unit movably locatable within a general path of the wafer handling system. Alternatively, the pre-alignment unit can be tilted with respect to a general path of the wafer handling system.
Still further, the buffer station additionally operates as a centering station for aligning a center of the at least one wafer with a center of the measurement location.
Moreover, in accordance with a preferred embodiment of the present invention, the robot includes a unit which simultaneously carries at least two wafers and the buffer station includes a unit which supports at least two wafers.
Additionally, in accordance with a preferred embodiment of the present invention, the processing station is one of the following types of processing stations: chemical-mechanical polisher, phototrack, exposure tool, etching equipment, physical vapor deposition tool and chemical vapor deposition tool.
Moreover, in accordance with a preferred embodiment of the present invention, the measuring unit is an integrated tool.
Further, in accordance with a preferred embodiment of the present invention, the buffer station includes one buffer unit. Alternatively, the buffer station includes at least two buffer units each of which is movable into and out of a general path of the wafer handling system. Alternatively, the buffer station includes three buffer units each of which is movable into and out of a general path of the wafer handling system. For the latter embodiment, the three buffer units include first, second and third buffer units, wherein the first and second buffer units and the second and third buffer units are separated by a predetermined distance and wherein the robot has two arms separated by the predetermined distance.
Finally, there is also provided, in accordance with a preferred embodiment of the present invention, a pre-alignment unit for a wafer measuring unit wherein the pre-alignment unit is tilted with respect to a plane of the wafer.